On a slightly related matter: the area51 front page (https://area51.phpbb.com/) now links to development packages of 3.0.x and 3.1.x called "nightly" builds. This should make testing 3.1.x a lot easier, basically download and install like 3.0.x.

The most interesting files are probably:

phpBB-$version.{zip,tar.bz2} for new installs, e.g. phpBB-3.1.0-dev.zip.